[racket] Macros With Multiple Ellipsis

Thanks guys.  I was going to use syntax/parse eventually anyway since the
final version will require syntax-classes etc, but I wanted to build a
simple version first since macros are still my nemesis :)


On Wed, Jan 8, 2014 at 12:33 PM, Stephen Chang <stchang at ccs.neu.edu> wrote:

> Yeah I'm pretty sure syntax-case won't let you do that.
>
> One solution is to use syntax-parse, which is (almost) a drop-in
> replacement for syntax-case (omit the list of literals), but with many
> additional features.
>
> #lang racket
> (require (for-syntax syntax/parse))
>
> (define-syntax (define/test stx)
>   (syntax-parse stx
>     [(_ (id arg ...) body ... #:test test-expr ...)
>      #'(define (id arg ...) body ... test-expr ...)]))
>
> (define/test (my-fn a b c)
>   (print a)
>   (print b)
>   (print c)
>   #:test
>   (print 'test1)
>   (print 'test2))
> (define-values (x y z) (values 10 20 30))
> (my-fn x y z)
>
> => 102030'test1'test2
>
> On Wed, Jan 8, 2014 at 2:58 PM, Scott Klarenbach <scott at pointyhat.ca>
> wrote:
> > I have a macro that modifies define to perform some additional
> processing.
> >
> > (define-syntax (define/test stx)
> >   (syntax-case stx ()
> > [(_ (id arg ...) body ... #:test test-expr)
> > #'(define (id arg ...) body ... test-expr)]))
> >
> > (define/test (my-fn a b c)
> >   (print a)
> >   (print b)
> >   (print c)
> >   #:test
> >   (print 'test))
> >
> > This works, but only if test-expr is one expression or wrapped in a
> begin or
> > something.  I'd like the test-expr to be the same as the define body.  I
> > wish I could write:
> >
> > (define-syntax (define/test stx)
> >   (syntax-case stx ()
> > [(_ (id arg ...) body ... #:test test-expr ...)
> >  #'(define (id arg ...) body ... test-expr ...)]))
> >
> > But I get a "misplaced ellipsis in pattern" error.
> >
> > I could change the pattern to something like (body ...) #:test (test-body
> > ...), but now the syntax of the macro has changed to include the extra
> > parenthesis.
> >
> > Am I making a simple mistake?  Or am I resigned to manually parsing out
> the
> > single test-expr into multiple forms in the template?
> >
> > Thanks.
> > --
> > Talk to you soon,
> >
> > Scott Klarenbach
> >
> > PointyHat Software Corp.
> > www.pointyhat.ca
> > p 604-568-4280
> > e scott at pointyhat.ca
> > 200-1575 W. Georgia
> > Vancouver, BC V6G2V3
> >
> > _______________________________________
> > To iterate is human; to recur, divine
> >
> > ____________________
> >   Racket Users list:
> >   http://lists.racket-lang.org/users
> >
>



-- 
Talk to you soon,

Scott Klarenbach

PointyHat Software Corp.
www.pointyhat.ca
p 604-568-4280
e scott at pointyhat.ca
200-1575 W. Georgia
Vancouver, BC V6G2V3

_______________________________________
To iterate is human; to recur, divine
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